Application Of Li-S Batteries Research Articles

Nanostructured CoS2-Decorated Hollow Carbon Spheres: A Performance Booster for Li-Ion/Sulfur Batteries

The practical application of Li-S batteries is being obstructed by severe safety concerns due to lithium dendrites. The Li-ion/sulfur battery, which uses Li2S as the cathode and can be coupled with...

Electrode Design with Integration of High Tortuosity and Sulfur-Philicity for High-Performance Lithium-Sulfur Battery

Summary Practical applications of Li-S batteries are hindered by the dissolution/diffusion loss of sulfur-related active materials in cathode and dendrite growth in Li metal anode. Here we present an integrated sulfur cathode design on tortuosity and sulfur-binding affinity parameters for mitigating diffusion loss of sulfur-based active materials. The high sulfur-philicity property (from oxygen functional groups, 16% in concentration) in reduced graphene oxide (rGO) host favors bonding with sulfur species to mitigate their diffusion/dissolution loss, while the high tortuosity (13.24, from horizontal arrangement of rGO sheets) can localize the soluble active materials within the host rather than outward diffusion loss with subsequent uneven redeposition. With this integrated concept, we achieved ultrahigh cathode areal capacities of 21 mAh cm−2 with 98.1% retention after 160 cycles, surpassing those electrodes with lower tortuosity and sulfur-philicity. In addition, same rGO host suppresses dendrite growth in Li anode, enabling 278% prolonged cycle life in the full cell.

In situ sulfur-doped graphene nanofiber network as efficient metal-free electrocatalyst for polysulfides redox reactions in lithium–sulfur batteries

Abstract The major challenge for realistic application of Li-S batteries lies in the great difficulty in breaking through the obstacles of the sluggish kinetics and polysulfides shuttle of the sulfur cathode at high sulfur loading for continuously high sulfur utilization during prolonged charge-discharge cycles. Here we demonstrate that large percentage of sulfur can be effectively incorporated within a three-dimensional (3D) nanofiber network of high quality graphene from chemical vapor deposition (CVD), through a simple ball-milling process. While high quality graphene network provided continuous and durable channels to enable efficient transport of lithium ions and electrons, the in-situ sulfur doping from the alloying effect of ball milling facilitated desirable affinity with entire sulfur species to prevent sulfur loss and highly active sites to propel sulfur redox reactions over cycling. This resulted in remarkable rate-performance and excellent cycling stability, together with large areal capacity at very high sulfur mass loading (Specific capacity over 666 mAh g−1 after 300 cycles at 0.5 C, and areal capacity above 5.2 mAh cm−2 at 0.2 C at sulfur loading of 8.0 mg cm−2 and electrolyte/sulfur (E/S) ratio of 8 µL mg−1; and high reversible areal capacities of 13.1 mAh cm−2 at a sulfur load of 15 mg cm−2 and E/S of 5 µL mg−1).

Rational design of perfluorinated sulfonic acid ionic sieve modified separator for high-performance Li-S battery

Practical application of Li-S battery is limited by the fast capacity decay and low coulombic efficiency caused by the shuttling phenomenon. Modification of the battery separator to impart the separator with ionic sieving property is an effective strategy to alleviate the shuttling phenomenon. In this study, perfluorinated sulfonic acid (PFSA) ionomers with different equivalent weight (EW) values are used to modify the commercial polyethylene separator, and the electrochemical performance of these separators is systematically investigated. Our results show that the separator modified using PFSA ionomer with a low EW value of 830 shows optimal battery performance owing to its unique structure of the ionic cluster. The Li-S battery with this modified separator shows an initial discharge capacity of 1352 mAh g−1 and a retained capacity of 931.6 mAh g−1 after cycling 100 times at 0.2 C, which demonstrates the effectiveness of this modification strategy. Furthermore, the correlation between the properties of PFSA ionomers and the electrochemical performance of the modified separator unveiled in this study may provide insight for the rational design of advanced separator for battery applications.

Uniform Polypyrrole Layer-Coated Sulfur/Graphene Aerogel via the Vapor-Phase Deposition Technique as the Cathode Material for Li-S Batteries.

The practical application of Li-S batteries is hampered because of their poor cycling stability caused by electrolyte-dissolved lithium polysulfides. Dual functionalities such as strong chemical adsorption stability and high conductivity are highly desired for an ideal host material for the sulfur-based cathode. Herein, a uniform polypyrrole layer-coated sulfur/graphene aerogel composite is designed and synthesized using a novel vapor-phase deposition method. The polypyrrole layer simultaneously acts as a host and an adsorbent for efficient suppression of polysulfide dissolution through strong chemical interaction. The density functional theory calculations reveal that the polypyrrole could trap lithium polysulfides through stronger bonding energy. In addition, the deflation of sulfur/graphene hydrogel during the vapor-phase deposition process enhances the contact of sulfur with matrices, resulting in high sulfur utilization and good rate capability. As a result, the synthesized polypyrrole-coated sulfur/graphene aerogel composite delivers specific discharge capacities of 1167 and 409.1 mA h g-1 at 0.2 and 5 C, respectively. Moreover, the composite can maintain a capacity of 698 mA h g-1 at 0.5 C after 500 cycles, showing an ultraslow decay rate of 0.03% per cycle.

In Situ Formed Li-B-H Complex Enables High-Performance Solid Electrolyte for Li Batteries

All-solid-state Li batteries are considered to be the next-generation high-density energy storage devices. The key material is the solid electrolyte with high Li-ion conductivity and wide electrochemical stability window. LiBH4 is considered as an alternative solid electrolyte due to its high conductivity (10-3 S cm-1 at 120 °C) and good electrochemical stability to Li anode. However, its main disadvantages are the low room temperature conductivity (< 10-7 S cm-1) due to the phase transformation at 110 °C and the poor electrochemical stability at high potential due to the strong reducibility. Searching for new types of Li borohydride beyond LiBH4 with superior Li-ion conducting properties is believed to be an effective strategy to push borohydride-based solid electrolytes towards practical applications. In this work, the Li-B-H complexes are facilely prepared via controllable dehydrogenation of LiBH4 as solid electrolytes for Li batteries. The Li-B-H complex with 7.5 wt% H2 desorption under 3 bar H2 (HP-LiBH2.4) shows exceptionally high Li-ion conductivity (2.7×10-4 S cm-1 at 35 °C) and low activation energy (0.43 eV). The Li-B-H complex possesses the best overall Li-ion conducting properties (in terms of Li-ion conductivity and electrochemical stability) among all borohydride-based solid electrolytes, and thus enables stable cycling of high capacity all-solid-state Li batteries at room temperature. In-depth characterizations demonstrate that the in situ formed interface layer between [Li2B12H11+1/n]n and LiBH4 is believed to be responsible for the high Li-ion conductivity. Moreover, this Li-B-H complex also exhibits excellent electrochemical stability, which enables the stable cycling of Li-TiS2 all-solid-state batteries at room temperature. Our results provide direct evidence for the exceptional Li-ion conductivity and electrochemical stability of Li-B-H complexes. This excellent performance plus the facile fabrication make this class of materials attractive for practical all-solid-state Li battery applications.

Carbon Nanofibers Modified By Natural Pectic Polysaccharide As the Multifunctional Interlayer for Advanced Li-SeS2 Batteries

In order to satisfy the ever-growing demand of higher energy densities for electric vehicles and consumer electronics, high-performance rechargeable batteries have attracted remarkable attentions in the last ten years. Recently, rechargeable Li-S batteries have captured intensive attention for high theoretical energy density and cost effective materials.[1] However, there is a certain distance to achieve the practical application of Li-S batteries due to some pivotal issues that are demanded of being disposed promptly: 1) the connatural poor electroconductivity of elemental sulfur and the end discharge products (Li2S/Li2S2), 2)a noticeable volume expansion in the lithiation process, 3) the shuttle effect of polysulfides (Li2Sn, 4≤n≤8).[2,3] Recently, researchers focus on the Se cathodes owing to the high electronic conductivity (1 X 10- 3 S m- 1) and the theoretical volumetric capacity (3253 mA h cm- 3) comparable to that of S (3467 mA h cm- 3). As the congener of S , Se has a similar (de)lithiation process to sulfur. However, the theoretical gravimetric capacity of Se (675 mA h g- 1) is much lower than that of S (1675 mA h g- 1).[4] To rationally balance the opposite but complementary features of Se and S, selenium sulfide (SeS2) has been proposed as a cathode for lithium ion batteries due to its theoretical mass capacity of 1345 mA h g- 1, which is close to that of sulfur, and its advantageous electronic conductivity as compared to sulfur. Since SeS2 has similar chemical properties to S, it is expected that the strategies used for stabilizing the S cathode might be also effective for suppressing the dissolution of lithium polysulfides/polyselenides in the SeS2 cathodes. To alleviate shuttling in high-sulfur-loading cathodes, improve sulfur utilization, and accelerate the redox reaction of polysulfides, a novel and advanced cell configuration has recently been developed by introducing a conductive interlayer between the sulfur cathode and the ordinary polymer separator. This inserted interlayer not only serves as an LPS trap, stabilizing LPSs within the cathode region, but also as a second current collector to reduce cell polarization and facilitate the redox kinetics.[5] In this contribution, pectic polysaccharide (named NPG), a natural polymer, is introduced to conductive carbon nanofibers (named CF) to build a free-standing CF-NPG composite interlayer via a solution-coating method. The pectic polysaccharide is isolated from the seed of Nicandra physaloides (L.) Gaertn by water extraction. The NPG have a backbone chain composed of 1→ 4 linked galacturonic acid with heavily branched glucose, galactose, and rhamnose side chains that can afford a strong binding interaction toward lithium polysulfdes and polyselenides through its rich hydroxyl, carboxyl, and ether functional groups.[6] Thus, the as-obtained CF-NPG composite interlayer can effectively impede the shuttle effect. In addition, the conductive composite interlayer, functioned as upper current collectors, can improve the SeS2 utilization, ensuring good cycling stability and rate capability. With the CF-NPG interlayers, the SeS2 cathodes with a high loading (70 wt%) demonstrat a good cyclability with a capacity retention of nearly 80% over 500 cycles. The SeS2 cathodes show excellent rate performances with capacities of 592 mA h g-1, 440 mA h g-1, and 350 mA h g-1 at 1A g-1, 5A g-1, and 10A g-1, respectively. In conclusion, a polysulfde-immobilizing polymer interlayer was firstly used for Li-SeS2 batteries, an effcient reuse of the adsorbed sulfides and selenides is realized and thus a high utilization of SeS2, which outperform most Li-SeS2 batteries reported in the literature. Figure 1 (a) the optical photographs of raw materials (nicandra physaloides seeds) (b) the SEM images of CF-PNG, (c) the cycle performance of SeS2 cathodes with CF-PNG interlayers. [1] Manthiram A, Fu Y, Su Y S. Challenges and prospects of lithium–sulfur batteries. Accounts of chemical research, 2012, 46(5): 1125-1134. [2] Liang X, Hart C, Pang Q, et al. A highly efficient polysulfide mediator for lithium–sulfur batteries. Nature communications, 2015, 6: 5682. [3] Fang R, Zhao S, Sun Z, et al. More Reliable Lithium‐Sulfur Batteries: Status, Solutions and Prospects. Advanced Materials, 2017, 29(48): 1606823. [4] He J, Lv W, Chen Y, et al. Direct impregnation of SeS 2 into a MOF-derived 3D nanoporous Co–N–C architecture towards superior rechargeable lithium batteries. Journal of Materials Chemistry A, 2018, 6(22): 10466-10473. [5] Guo Y, Zhang Y, Zhang Y, et al. Interwoven V 2 O 5 nanowire/graphene nanoscroll hybrid assembled as efficient polysulfide-trapping-conversion interlayer for long-life lithium–sulfur batteries. Journal of Materials Chemistry A, 2018, 6(40): 19358-19370. [6] Niu Q F, Wang B, Li T, et al. Structure and Gel Characterizaction of Petic Polysaccharide from Nicandra physaloides (L.) Gaertn Seeds. Modern Food Science and Technology, 2015, 9: 68-73. Figure 1

Reduction of Interfacial Polarization between Inorganic Solid Electrolyte and Li Anode By Using a Metallic Interlayer

In early 1990s, rechargeable batteries using inorganic ionic conductors as solid electrolytes have been proposed. Because of their improved safety features, solid state batteries have received great attention recently. Among several inorganic ionic conductors, Garnet-structured Li7La3Zr2O12 (LLZO) show adequate ionic conduction and excellent structural stability when used as the solid electrolyte for Li battery applications. Using Li metal as anode has been a long-term target Moreover, LLZO exhibits superior reduction stability against metallic Li. However, the poor contact/adhesion between Li and LLZO has caused large interface polarization between LLZO and Li metal. Several metals and oxides have been used as the interlayer between LLZO and Li metal and shown improved interface behaviour with lower polarization. Sputtering has been an excellent thin-film deposition technique for obtaining metallic and oxide thin film. Thus, the main objective of this study is to (i) investigate the feasibility of using metallic thin film as an interlayer for inorganic solid state battery using Li as anode, (ii) to evaluate the interface polarization with and without interlayer; (iii) to determine the effect of interlayer thickness on interface polarization, (iv) to analyse and understand the process and behaviour of Li insertion into metal thin film layer, (v) to demonstrate the effectiveness of metallic interlayer on reduction of interface polarization based on Li stripping/plating and full cell tests. In this study, LLZO will be densified to >95% dense using nanosized powder. Gold thin film will be first deposited on the polished surface of LLZO using rf magnetron sputtering. Secondly, Li metal will be placed on top of Au film under heating near melting point of Li. Li stripping and plating will be conducted under constant current with monitoring of applied voltage. Impedance resulted from interface variation will be measured using Electrochemical impedance spectroscopy (EIS). XRD analysis and SEM observation will be performed for possible alloy forming processing. Finally, a full cell based on Li/Au (interlayer)/LLZO/LCO will be tested and compared with the one without Au interlayer to show the effectiveness of metallic interlayer.

Fabrication and Characterization of Fine-Grained Nasicon-Structured Li Electrolyte for Solid State Batteries Applications

Rechargeable batteries using inorganic ionic conductors as solid electrolytes have been proposed over decades. Due to their improved safety features, solid state batteries have received great attention recently. Among several inorganic ionic conductors, NASICON-structured Li1+xAlxTi2-x(PO4)3 (LATP) show excellent ionic conduction and adequate structural stability when used as the solid electrolyte for Li battery applications. However, the physical properties of solid electrolyte may be affected by their chemical composition and processing parameters. Thus, the objective of this study is (i) to investigate the effect of grain size on the electrical properties, (ii) to lower interface polarization of layered oxide cathode/electrolyte, (iii) to examine the effect of microstructure variation on cathode/solid electrolyte performance. In this study, the ceramic self-standing thick films of Li- NASICON with composition Li1.3Ti1.7Al0.3(PO4)3 by tape casting were prepared. A full cell using layered oxide/graphite (or Li metal) as the cathode/anode separated by LATP were assembled and tested A complete characterization of the samples including structural, microstructural, impedance as well as the electrochemical testing were conducted. Due to dependence of grain-size on ionic conduction, more discussion will focus on the contribution of both the grain boundary and the "bulk" conductivity. Microstructure will be varied by creation of different pore size and porosity in order to search for better electrode configuration.

Carbon nanotubes/SiC prepared by catalytic chemical vapor deposition as scaffold for improved lithium-sulfur batteries

The low conductivity of sulfur and shuttle effect of lithium polysulfides have limited the applications of Li-S batteries. In this account, carbon nanotubes/SiC (CNTs/SiC) composites were prepared by means of catalytic chemical vapor deposition (CCVD). SiC was used as the matrix for growth of CNTs and ferrocene served as catalyst. The surface of SiC was successfully loaded with carbon nanotubes, which underwent increasing growth to form clusters. Sulfur was added into CNTs/SiC by the hydrothermal method to yield sulfur-carbon nanotubes/SiC composites (S-CNTs/SiC) for Li-S batteries. SiC was strongly bound to lithium polysulfides (LPS) through chemical interactions and CNTs attracted LPS by physical absorption. CNTs provided good electrical conductivity for the overall composite and SiC enhanced adsorption ability of LPS. DFT calculation was carried out to illustrate direct Si-S interaction and strong confinement on LPS of SiC. Both factors synergistically reduced loss in active substances during battery cycling. The resulting S-CNTs/SiC electrodes displayed discharge capacity of 685 mAh g−1 at 0.1 C after 100 cycles, coupled with excellent cycle performance of 316 mAh g−1 after 400 cycles at 1 C.

Waste to Wealth: Exhausted Nitrogen-Doped Mesoporous Carbon/MgO Desulfurizers Turned to High-Sulfur-Loading Composite Cathodes for Li-S Batteries.

We demonstrate a sustainable and cost-effective route to fabricate high-sulfur-loading cathode materials with the cooperative interfaces of "sulfiphilic" and "lithiophilic" sites from the removal industry of the pollutant H2S gas. The MgO-impregnated and nitrogen-doped mesoporous carbon composite desulfurizers (NMC/MgO), acting as effective catalysts and large storehouses, could catalytically oxidize H2S into elemental S with high catalytic selectivity and sulfur capacity. The obtained byproduct NMC/MgO/S-CO composites possess high sulfur loading (73.8 wt %) and significant structure advantages for practical application in Li-S batteries. First, the uniform distribution of S in the NMC/MgO frameworks via the in situ catalytic oxidation approach could offer large interface area for charge transport and Li+ reaction. Then, the cooperative effects of the "sulfiphilic" MgO nanoparticles and the "lithiophilic" nitrogen dopants in the NMC/MgO could effectively suppress the polysulfide shuttling. Under the further assistance of physical confinement of the mesoporous NMC/MgO, the NMC/MgO/S-CO composites present excellent electrochemical performances with a high reversible capacity of 772 mAh g-1 and a Coulombic efficiency of 93.6% at the 100th cycle at 0.2 C. These encouraging results not only develop a sustainable way to turn waste into wealth but also provide a promising strategy to product high-sulfur-loading cathode materials with uniform distribution of S through the in situ catalytic strategy for high-performance Li-S batteries.

Deposition of thin δ-MnO2 functional layers on carbon foam/sulfur composites for synergistically inhibiting polysulfides shuttling and increasing sulfur utilization

Practical application of LiS battery is greatly impeded by the critical challenges of large volume expansion, intrinsic insulation problem of active materials, and serious polysulfides shuttling. Thus, it is still quite essential for us to search an efficient strategy to synergistically overcome these problems. Herein, we design and in-situ deposit a functional δ-MnO2 layer onto the outside surface of porous carbon foam/sulfur composites to synergetic inhibit the polysulfides shuttling and increase sulfur utilization, finally improve the electrochemical performance of LiS batteries. As verified by UV–vis and XPS results, the strong chemical interaction between the MnO2 layer and polysulfide intermediates is characterized to be an internal disproportionation reaction by transferring the absorbed long-chain polysulfides into insoluble polythionate complex. Also, the unique structure possesses high conductivity and good volume expansion tolerance, further guaranteeing the electrode a good cycling stability, rate performance and low self-discharge behavior. The MnO2 coated carbon foam/S electrode displays a remarkable capacity of 1547 mA g−1 at 0.1 C, and achieves a reversible capacity of 629 mA g−1 after 300 cycles at 1 C. Even with sulfur loading of 2.6 and 4.3 mg cm−2, the designed electrodes still deliver an initial discharge capacity of 1106 and 963 mA g−1 at 0.2 C.

Probing the Interactions and Dynamics in an Ionic Liquid – Organic Solvent Hybrid Electrolyte System for Potential Application in Li-S Batteries

The depletion of fossil fuel and strict environmental regulation on carbon footprints has prompted a greater reliability on sustainable energy sources. Batteries represent an important energy storage option due to their wide range of applicability and portability, however, for certain applications such as transportation, a higher energy density battery is required. Beyond the conventional Li-ion battery system, current research is focusing on next-generation cost effective devices. Amongst them, the Li-S battery technology is very promising due to its high theoretical capacity and energy density [1]. However, the chemistry involved in the Li-S battery is a complex process with multiple consecutive electrochemical reactions. Despite having many advantages, its application is still limited by several issues, e.g., the dissolution and diffusion of intermediate polysulphides, unstable plating and stripping of Li metal, both resulting in rapid capacity fading [2]. Previously, we reported the application of a novel electrolyte system composed of N-propyl-N-methylpyrrolidinium bis(fluorosulfonyl)imide, C3mpyrFSI, ionic liquid (IL) and 1,2 dimethoxyethane (DME) in the presence of varying saturated lithium bis(fluorosulfonyl)imide, LiFSI which predominantly suppressed the polysulphide dissolution and diffusion while showing improved lithium plating and stripping behavior [3]. In order to expand our understanding on the role of DME and the lithium salt concentration; in this work, we have considered a similar ionic liquid based electrolyte system but at a constant concentration of LiFSI salt. The ionic interactions among different species of the electrolyte system have been extensively studied by nuclear magnetic resonance (NMR) spectroscopy using 1D chemical shift, PFG-NMR and Heteronuclear Overhauser Effect SpectroscopY (HOESY) measurements. We found that, when increasing the DME concentration in the system, a strong association of Li+ cation with the DME occurs due to the electronegative oxygen atoms present in the DME molecules which leads to strong coordination. This leads to a change of the chemical shift of 7Li nuclei due to them being increasingly de-shielded. Interestingly, we found that the diffusivity of both Li+ and DME species are very similar, which also confirms that a Li-DME complex is present with FSI anion associated in the next coordination sphere to counterbalance the positively charged Li complex. MD simulations are underway to better elucidate the molecular shell structure of the system. We have also carried out electrochemical characterizations of these hybrid electrolytes to determine their potential applicability in a lithium sulphur battery. It was apparent using cyclic voltammogram (CV) performed in a three electrode set-up, that an increasing amount of DME increases the ionic conductivity but decreases the lithium plating-stripping efficiency. A coin-cell study of Li/Li symmetrical cycling showed an excellent plating-stripping behaviour for 70%IL-30%DME composition. We have carried out a full cell cycling against sulphur cathode and the optimised electrolyte composition obtained a promising first discharge capacity of 1100mAh/g. Additionally, we have investigated the sulphur speciation in the presence of this ionic liquid in a three-electrode system where platinum mesh has been used as working electrode coupled with in-situ UV-vis spectroscopy. Finally, a time dependent bulk electrolysis study revealed the plausible intermediates formed during the charge-discharge cycle of sulphur redox reaction. From these studies it appears that the composition of this novel hybrid electrolyte system can be tuned to provide a system with improved transport, electrochemical and sulphur speciation properties which lend themselves to a higher performance, next generation lithium sulphur battery technology.

High-performance lithium−sulfur batteries fabricated from a three-dimensional porous reduced graphene oxide/La2O3 microboards/sulfur aerogel

Rechargeable lithium–sulfur (Li–S) batteries are a promising energy storage device because of their high energy density, but the poor electrical conductivity of the sulfur cathode and the polysulfide-shuttle effect still hinder the application of Li-S batteries. Herein, with the aid of compositional and structural design and the use of a controllable one-pot hydrothermal method, a three-dimensional (3D) porous reduced graphene oxide@La2O3@S (r-GO@La2O3@S) composite is fabricated for use as the cathode material of Li–S batteries. In this 3D porous structure, the effective adsorption ability of the La2O3 microboards toward the polysulfides, based on strong chemical binding, and the conductivity of r-GO provide pathways to facilitate electron and ion transport while being able to accommodate the volume expansion/contraction of the sulfur cathode during the discharge-recharge processes. The r-GO@La2O3@S cathode delivers an initial reversible capacity of 1227.4 mAh g−1 and remains 668.3 mAh g−1 at 0.2 C after 200 cycles. At a higher current of 1 C, the capacity retention remains higher than 73% of the initial capacity after 100 cycles, indicating the excellent electrochemical properties of the cathode. The exceptional performance is attributed to the synergistic effects of the conductive r-GO and La2O3 microboards with the active sulfur.

Spider-Web-Inspired Nanocomposite-Modified Separator: Structural and Chemical Cooperativity Inhibiting the Shuttle Effect in Li-S Batteries.

Despite their high theoretical capacity density (1675 mAh g-1), the application of Li-S batteries has been seriously hindered by the shuttle effect of polysulfides. Here, inspired by the working principle of natural spider webs, we synthesized a spider-web-like nanocomposite in which many hollow mesoporous silica (mSiO2) nanospheres/Co nanoparticles were threaded by interconnected nitrogen-doped carbon nanotubes (NCNTs). Then the nanocomposite (denoted as Co/mSiO2-NCNTs) was coated on the commercial separator by a simple infiltration to mitigate the above issue. The intimate combination of three-dimensional conductive networks (NCNTs) with abundant polysulfide adsorbent sites (SiO2 and N)/polysulfide conversion catalysts (Co and Co-N x species) allows the Co/mSiO2-NCNTs coating layer to not only effectively capture polysulfides via both physical confinement and chemical bonding but also accelerate the redox kinetics of polysulfides significantly. Furthermore, the combination of ex situ experiment and theoretical calculation demonstrates that the reversible adsorption/desorption of polysulfides on mSiO2 nanospheres benefits uniform deposition of Li2S2/Li2S on the conductive networks, which contributes to long-term cycling stability. As a result, Li-S batteries with Co/mSiO2-NCNTs-coated separators exhibited both excellent cycling stability and rate performance.

氮掺杂石墨烯海绵的可控合成及其在锂硫电池中的应用

氮掺杂石墨烯海绵的可控合成及其在锂硫电池中的应用

Enhancing the cycle life of Li-S batteries by designing a free-standing cathode with excellent flexible, conductive, and catalytic properties

Poor electrical conductivity of sulfur, sluggish redox kinetics, dissolution of intermediate polysulfides, and expansion in volume upon cycling are the main drawbacks that hamper the practical application of Li-S batteries. By taking advantages of the high conductivity and favorable catalytic activity of RuO2, we design a 3D carbon nanotube film with embedded RuO2 nanoparticles as a freestanding type of chemisorptive and catalyst-like cathode for Li-S batteries, which can be facilely prepared by a surfactant-assisted vacuum infiltration method. Both experimental and theoretical results reveal the excellent capability of RuO2 for anchoring polysulfides and accelerating the kinetics of polysulfides catalytic redox reactions. Besides, the 3D freestanding cathode is beneficial to overcoming pulverization during volume changes, especially for long-term cycling. At a high areal sulfur loading of 2 mg cm−2, favorable initial capacities of 750 and 1060 mA h g−1 respectively at 2 and 0.5 C are achieved. More attractively, the capacity after 1000 cycles maintains 405 mA h g−1 at 0.5 C with a loss in capacity of only 0.06% per cycle. Additionally, such freestanding cathode allows the batteries to be tested under various bending stages, hence encouraging more research works on fabrication of other 3D nanostructure families as high-performance cathodes for Li-S batteries.

Polar and conductive iron carbide@N-doped porous carbon nanosheets as a sulfur host for high performance lithium sulfur batteries

The practical application of Li-S batteries is inherently limited by the low conductivity of sulfur and the dissolution of polysulfides. The enhancement of conductivity and introduction of polarity to the sulfur host is an effective strategy to overcome these long-standing challenges. In this work, a facile one-step carbonizing process is used to synthesize a unique porous and conductive nanocomposite where Fe3C nanoparticles are embedded in nitrogen-doped porous carbon sheets (Fe3C@NPCS). As demonstrated in Li2S4 adsorption experiments and confirmed by density functional theory calculations, Fe3C nanoparticles are able to strongly adsorb polysulfides via strong Fe-S chemical bonds. Due to the remarkable conductivity, Fe3C nanoparticles can also accelerate the electrochemical reactions of the polysulfides through fast electron transportation. The carbon sheets prevent the aggregation of Fe3C nanoparticles and accommodate sulfur and its volume expansion during charge/discharge processes. With these features, the resultant sulfur cathodes (Fe3C@NPCS-S) deliver an excellent cycling performance with a capacity decay of 0.036% per cycle, and high rate performance of ca. 1127, 1020, 907, 802, 731 and 647 mAh g−1 under current densities of 0.3, 0.5, 1, 2, 3 and 5 C, respectively.

Bioinspired Polysulfiphobic Artificial Interphase Layer on Lithium Metal Anodes for Lithium Sulfur Batteries.

The application of Li-S batteries suffers from many issues, polysulfide dissolution in particular. The fresh Li metal reacts with polysulfide continuously, which aggravates irregular Li plating/stripping behavior and decomposition of organic electrolyte resulting in short cycle life and low Coulombic efficiency. Nature has provided a lot of inspiration for human to realize structural construction and functional integration, as it does to battery design. In this report, learning from the hydrophobic property of natural species, a scaly polysulfiphobic artificial interphase layer are constructed on lithium metal anodes that can repel LiPS through the functional decylphosphonate groups that are proved by in operando XPS with Ar ion sputtering. Moreover, the obtained artificial interphase layer keeps dendrite-free morphology and restrains side reactions during cycling effectively. In situ XRD measurements are employed to demonstrate the inhibiting effect for decomposition of organic electrolyte. The as-obtained LDP-Li anodes exhibit outstanding electrochemical performance with the specific capacity of ∼1000 mAh g-1 corresponding to Coulombic efficiency of nearly 99%, which shows great promise for the application of Li-S batteries.

Ultra-thin Fe3C nanosheets promote the adsorption and conversion of polysulfides in lithium-sulfur batteries

Rational design of hierarchical porous materials with comprehensive properties, e.g. good conductivity, fine dispersibility for sulfur, strong adsorption and catalytic abilities to polysulfides (LiPSs), is urgently needed for the practical application of lithium-sulfur batteries (Li-S batteries). Here, based on density functional theory (DFT) computational results and the design concept of efficient, low-cost and environmental friendliness, we report an ultra-thin (~ 1 nm) Fe3C nanosheets growing on mesoporous carbon (Fe3C-MC) with large specific surface area of 686.9 m2 g-1 and pore volume of 6.52 cm3 g-1. Meanwhile, the formation mechanism of two-dimensional Fe3C is revealed according to DFT results. In the Fe3C-MC composite, the mesoporous carbon constructs a conductive network for dispersion of sulfur species, while Fe3C nanosheets play a key role in electronic transmission, LiPSs adsorption and conversion in Li-S batteries. As a result, the Fe3C-MC composite delivers a high initial capacity of 1530 mA h g-1 at 0.1 C, and a capacity of 699 mA h g-1 after 100 cycles at 0.5 C at a super-high sulfur loading of 9.0 mg cm-2, meaning a specific area capacity of 6.291 mA h cm-2. Such sulfur host is expected to accelerate the practical applications of Li-S batteries benefiting from the low-cost and large-scale process.